Sprinkler systems are used to water agricultural areas, and larger municipal and residential areas. Such a system typically includes a plurality of sprinklers interconnected by one or more water supply lines, which, in turn, are connected to a water source. A typical sprinkler includes a hollow housing coupled to the water supply and an outlet nozzle for directing a spray of water in a desired pattern. Frequently the nozzle is carried on a "pop-up" riser which is spring biased to a retracted position within the housing, and pops out of the housing when sufficient water pressure is applied to the sprinkler. In order to permit the riser to move between an extended water application position and the retracted position within the housing, a slight gap exists between the exterior surface of the riser and the interior surface of the housing about its upper end.
Seal elements have been inserted in the gap in order to prevent dirt and other undesirable extraneous material from entering through the gap into the interior of the housing. One type of prior art riser seal is formed of a relatively stiff flat piece of rubber. The flat piece of rubber is inserted at the top of the housing in its normal flat configuration and a removable top is secured above the seal element to hold it on top of the housing. Since the seal element is held in a flat condition, its entire inner edge contacts the exterior surface of the riser in the normal position of the seal element. Such edge contact results in a fair amount of interference between the seal element and the riser body. However, during retracting motion of the riser, the seal element bends downward away from the edge contact position to a position where the interference between the seal element and the riser body is reduced. Reduction of interference during retraction of the riser body is undesirable because the interference of the seal element on the riser body performs a wiping function to remove dirt from the riser body. It is also desirable to place the seal element as close as possible to the ground line, i.e., as close to the top of the sprinkler as possible, so that a minimum amount of area is present in the gap above the seal into which dirt can accumulate. In this type of prior seal element, the removable top must be made relatively thin and, hence, somewhat weak in order to accomplish this objective.
Another type of prior art seal element is molded directly into the removable top or cap. This seal element is formed of relatively rigid rubber or rubber-like material and includes a relatively thick ring-shaped section molded into the cap, and a vertical section extending upward and downward from the ring-shaped section. The vertical section includes upper and lower sealing tips which contact the riser element. While this type of seal element accomplishes the objective of placing the seal element near the ground line, without weakening the removable cap, its shape and construction technique are relatively complicated and expensive.
To date, no prior art seal has been developed which accomplishes the objective of locating a riser seal element near the ground line in a reliable, relatively inexpensive manner, without adversely affecting the strength of the removable top.